It is known that various functions can be imparted to a vinyl polymer by introducing various functional groups to the molecular terminals of said vinyl polymer and utilizing said functional groups by, for example, crosslinking said vinyl polymer or formulating the same into dispersed particles.
According to JP-B-43-16147 (the term "JP-B" as used herein means an "examined Japanese patent publication"), for example, an acrylic copolymer having an carboxyl group at a molecular terminal is synthesized by using 4,4'-azobis(cyanovaleric acid) and thioglycolic acid as a polymerization initiator and a chain transfer agent respectively in order to stabilize or crosslink said copolymer.
To obtain a hydrolyzable silyl group-containing vinyl copolymer, on the other hand, we have proposed to use a mercaptoalkylsilane as a chain transfer agent (JP-A-57-36109 (the term "JP-A" herein means an "unexamined published Japanese patent application"). However this method has disadvantages. For example, when the chain transfer agent is used alone, the amount of the hydrolyzable silyl groups which can be introduced into the molecular end of the vinyl polymer is limited. Further, the use of a large amount of the mercaptoalkylsilane would lower the weathering resistance of the resulting vinyl polymer.
We have conducted extensive studies in order to solve the above problems. As a result, we have completed the present invention.